1. Technical Field
Embodiments of the invention pertain generally to improvements in methods for sequencing data through a routing device. More particularly, embodiments pertain to a method for scoring queued frames for selective transmission through a switch. Embodiments are particularly, but not exclusively, useful for selectively transmitting frames through a fibre channel switch.
2. Relevant Background
Computer performance during the past decade has increased significantly, if not exponentially, in part driven by the information explosion. Consequently, demand for high-performance communications for server-to-storage and server-to-server networking also has increased. Performance improvements in hardware entities, including storage, processors, and workstations, along with the move to distributed architectures such as client/server, have increased the demand for data-intensive and high-speed networking applications. The interconnections between and among these systems, and their input/output devices, require enhanced levels of performance in reliability, speed, and distance.
Simultaneously, demands for more robust, highly available, disaster-tolerant computing resources, with ever-increasing speed and memory capabilities, continues unabated. To satisfy such demands, the computer industry has worked to overcome performance problems often attributable to convention I/O (“input/output devices”) subsystems. Mainframes, supercomputers, mass storage systems, workstations and very high-resolution display subsystems frequently are connected to facilitate file and print sharing. Because of the demand for increased speed across such systems, networks and channels conventionally used for connections introduce communication clogging, especially if data is in large file format typical of graphically based applications.
Efforts to satisfy enhanced performance demands have been directed to providing storage interconnect solutions that address performance and reliability requirements of modern storage systems. At least three technologies are directed to solving those problems SCSI (“Small Computer Systems Interface”); SSA (“Serial Storage Architecture”), a technology advanced primarily by IBM; and Fibre Channel, a high performance interconnect technology.
Two prevalent types; of data communication connections exist between processors, and between a processor and peripherals. A “channel” provides direct or switched point-to-point connection communicating devices. The channel's primary task is to transport data at the highest possible data rate with the least amount of delay. Channels typically perform simple error correction in hardware. A “network”, by contrast, is an aggregation of distributed nodes. A “node” as used in this document is either an individual computer or similar machine in a network (workstations, mass storage units, etc.) with a protocol that supports interaction among the nodes. Typically, each node must be capable of recognizing error conditions on the network and must provide the error management required to recover from the error conditions.
SCSI is an “intelligent” and parallel I/O bus on which various peripheral devices and controllers can exchange information. Although designed approximately 15 years ago, SCSI remains in use. The first SCSI standard, now known as SCSI-1, was adopted in 1986 and originally designed to accommodate up to eight devices at speeds of 5 MB/sec. SCSI standards and technology have been refined and extended frequently, providing ever faster data transfer rates up to 40 MB/sec. SCSI performance has doubled approximately every five years since the original standard was released, and the number of devices permitted on a single bus has been increased to 16. In addition, backward compatibility has been enhanced, enabling newer devices to coexist on a bus with older devices. However, significant problems associated with SCSI remain, including, for example, limitations caused by bus speed, bus length, reliability, cost, and device count. In connection with bus length, originally limited to six meters, newer standards requiring even faster transfer rates and higher device populations now place more stringent limitations on bus length that are only partially cured by expensive differential cabling or extenders.
Accordingly, industry designers now seek to solve the limitations inherent in SCSI by employing serial device interfaces. Featuring data transfer rates as high as 200 MB/sec, serial interfaces use point-to-point interconnections rather than busses. Serial designs also decrease cable complexity, simplify electrical requirements, and increase reliability. Two solutions have been considered, Serial Storage Architecture and what has become known as Fibre Channel technology, including the Fibre Channel Arbitrated Loop (“FC-AL”).
Serial Storage Architecture is a high-speed serial interface designed to connect data storage devices, subsystem, servers and workstations. SSA was developed and is promoted as an industry standard by IBM; formal standardization processes began in 1992. Currently, SSA is undergoing approval processes as an ANSI standard. Although the basic transfer rate through an SSA port is only 20 MB/sec, SSA is dual ported and full-duplex, resulting in a maximum aggregate transfer speed of up to 80 MB/sec. SSA connections are carried over thin, shielded, four-wire (two differential pairs) cables, that are less expensive and more flexible than the typical 50- and 68-conductor SCSI cables. Currently, IBM is the only major disk drive manufacturer shipping SSA drives; there has been little industry-wide support for SSA. That is not true of Fibre Channel, which has achieved wide industry support.
Fibre Channel (“F/C”) is an industry-standard, high-speed serial data transfer interface used to connect systems and storage in point-to-point or switched topologies. FC-AL technology, developed with storage connectivity in mind, is a recent enhancement that also supports copper media and loops containing up to 126 devices, or nodes. Briefly, fibre channel is a switched protocol that allows concurrent communication among workstations, super computers and various peripherals. The total network bandwidth provided by fibre channel may be on the order of a terabit per second. Fibre channel is capable of transmitting frames along lines or lanes at rates exceeding 1 gigabit per second in at least two directions simultaneously. F/C technology also is able to transport commands and data according to existing protocols such as Internet protocol (“IP”), high performance parallel interface (“HIPPI”), intelligent peripheral interface (“IPI”), and, as indicated using SCSI, over and across both optical fiber and copper cable.
The fibre channel may be considered a channel-network hybrid. An F/C system contains sufficient network features to provide connectivity, distance and protocol multiplexing, and enough channel features to retain simplicity, repeatable performance and reliable delivery. Fibre channel allows for an active, intelligent interconnection scheme, known as a “fabric”, and fibre channel switches to connect devices. The F/C fabric includes a plurality of fabric-ports (F_ports) that provide for interconnection and frame transfer between plurality of node-ports (N_ports) attached to associated devices that may include workstations, super computers and/or peripherals. A fabric has the capability of routing frames based on information contained within the frames. The N_port transmits and receives data to and from the fabric.
Transmission is isolated from the control protocol so that different topologies (e.g., point-to-point links, rings, multidrop buses, and crosspoint switches) can be implemented. Fibre Channel, a highly reliable, gigabit interconnect technology allows concurrent communications among workstations, mainframes, servers, data storage systems, and other peripherals. F/C technology provides interconnect systems for multiple topologies that can scale to a total system bandwidth on the order of a terabit per second. Fibre Channel delivers a new level of reliability and throughput. Switches, hubs, storage systems, storage devices, and adapters designed for the F/C environment are available now.
Following a lengthy review of existing equipment and standards, the Fibre Channel standards group realized that it would be useful for channels and networks to share the same fiber. (The terms “fiber” or “fibre” are used synonymously, and include both optical and copper cables.) The Fibre Channel protocol was developed and adopted, and continues to be developed, as the American National Standard for Information Systems (“ANSI”). See Fibre Channel Physical and Signaling Interface, Revision 4.2, American National Standard for Information Systems (ANSI) (1993) for a detailed discussion of the fibre channel standard, that is incorporated by reference into this document.
Current standards for F/C support bandwidth of 133 Mb/sec, 266 Mb/sec, 532 Mb/sec, 1.0625 Gb/sec, and 4 Gb/sec (proposed) at distances of up to ten kilometers. Fibre Channel's current maximum data rate is 100 MB/sec (200 MB/sec full-duplex) after accounting for overhead. In addition to strong channel characteristics, Fibre Channel provides powerful networking capabilities, allowing switches and hubs to interconnect systems and storage into tightly knit clusters. The clusters are capable of providing high levels of performance for file service, database management, or general purpose computing. Because Fibre Channel is able to span up to 10 kilometers between nodes, F/C allows very high-speed movement of data between systems that are greatly separated from one another. The F/C standard defines a layered protocol architecture consisting of five layers, the highest layer defining mappings from other communication protocols onto the F/C fabric.
The network behind the servers link one or more servers to one or more storage systems. Each storage system could be RAID (“Redundant Array of Inexpensive Disks”), tape backup, tape library, CD-ROM library, or JBOD (“Just a Bunch of Disks”). One type of RAID system divides each byte of data into bits and stores each bit on a different disk. If the data consists of S-bit bytes, there will be 10 disks, one for each of the 8 bits, and two more for an error-correcting code. The error-correcting code makes it possible to reconstruct any single missing bit in any byte. Thus, if one of the disk drives fails completely, only one bit will be missing from each byte, and the contents of the failed disk can be reconstructed completely from the error-correcting code.
Fibre Channel networks have proven robust and resilient, and include at least these features: shared storage among systems; scalable networking; high performance; fast data access and backup. In a Fibre Channel network, legacy storage systems are interfaced using a Fibre Channel to SCSI bridge. Fibre Channel standards include network features that provide required connectivity, distance, and protocol multiplexing. It also supports traditional channel features for simplicity, repeatable performance, and guaranteed delivery.
The demand for speed and volume of transmission has generated a concomitant demand for a capability to sort data to enable a user to identify data and data streams that have higher priority than other data queued in devices for routing data, such as a switch, particularly a fibre channel switch. It would be useful, therefore, to be able to order, or sequence, transmission of data through a fibre channel switch, including frames, based on the content of the frame as well as the source of the frame by assigning a score to data received by a device such as a switch, and to be able to transmit data and frames having the highest score.
Currently, therefore, a previously unaddressed need exists in the industry for a new, useful and reliable method for scoring queued frames for selective transmission through a switch, particularly in a Fibre Channel environment. It would be of considerable advantage to provide a method for assigning scores to data frames received by a switch, and to selectively expedite transmission of the frames having the highest score.